#include<iostream> 
#include<stdio.h>
#include<string.h>
//#include<cmath>
#include<conio.h>
using namespace std;
int main()
{
    int n;
    char ch1[50],ch2[50],ch3[50];
    char c;
    while(scanf("%d",&n)!=EOF)
    {
         int sum1=0;
         //zzz->first
         cin>>c>>ch1>>c>>ch2>>c>>ch3;
         if(n==0) {cout<<0<<endl;continue;}
         for(int i=0;i<n;i++)
           if(ch1[i]!=ch2[i]) sum1++;
         for(int i=0;i<n;i++)
           if(ch1[i]!=ch3[i]) sum1++;
         cout<<sum1<<endl;
         cin>>c;
         //getchar();
    }
    //system("pause");
    return 0;
}
